Many applications require the ability to continuously point a device, often referred to as a payload, at an object as that object moves relative to the device. Examples of such applications include satellite-mounted equipment, solar arrays, telescopes, turrets, antennas, wind turbines, radar, satellite dishes, robotic end effectors, security cameras, sporting event cameras and webcams. These applications typically require active payload devices, which have electrical, microwave, fluid, or other types of connections. These connections are typically made between the moving payload and a fixed base, around which the payload rotates in one or more axes while tracking. To prevent twisting of these connections, existing solutions either use electrical slip rings or rotary fluid couplings for uninterrupted motion, or must unwind after a certain number of rotations, leading to an inability to continuously track the object of interest. For example, current solutions for radio antennas, such as Stanford University's 150 foot diameter radio telescope known as “The Dish,” are only able to rotate twice about their azimuth direction before they have to unwind their cables. Therefore, antennas such as these are unable to continually track an overhead object. Similarly, more terrestrial devices such as camera mounts and gun turrets are unable to continuously track an object without twisting cables or other connections.
The use of “CubeSats” is another example of an application in which it is desirable to continuously track an object without twisting connections. A CubeSat is a type of miniaturized satellite for space research that usually has a volume of exactly one liter (10 cm cube), has a mass of no more than 1.33 kilograms, and typically uses commercial off-the-shelf electronics components. With CubeSats continuing to gain popularity in both educational and commercial satellite markets, the capabilities and requirements of these satellites are growing as well. The fixed solar panels and batteries that could handle the power requirements of earlier CubeSats are inadequate for emerging high-power larger CubeSats. Given the volume and mass constraints of the CubeSat design specification, adding more solar panels is often not an option, thus designs must maximize the efficiency of their panels. The power that a solar panel can generate is proportional to the projected area and orientation along the vector towards the Sun. Therefore, it is vital to orient the panels normal to the Sun for maximum efficiency. This presents a major challenge not only in CubeSats but also in larger satellites. Most satellites in a geosynchronous orbit (GSO) use a simple 1 degree of freedom (DOF) solar tracking system that provides adequate performance. However, in low earth orbit (LEO) applications, 2 or higher DOF systems are needed to efficiently track the sun throughout an entire orbit. It is therefore highly desirable to produce a system that can rotate a solar panel array through an entire hemisphere by varying both a rotation and elevation angle from the satellite, while minimizing system complexity. For a CubeSat application, the system should also take up no more than about half of the volume of the satellite (0.5 U, or 10 cm×10 cm×5 cm) when stowed, as tracking systems larger than this would greatly limit the remaining available payload volume.
What is needed and is not provided by the prior art is a low complexity, low volume, low mass and low cost system that allows for continuous positioning of an object without twisting its connections.